\section{Task environment}
	
	\subsection{Agent types}
	
		There are several types of intelligent agents :
		\begin{itemize}
			\item Reactive
			\item Model based
			\item Goal based
			\item Utility based
			\item Learning agents
		\end{itemize}
		
		Of course, these types could be mixed.
		
		\paragraph{Reactive agent\\}
		A reactive agent use only stimuli - response. It can be described by if-then rules but in practice it's by continuous functions. It's the most simple agent but it can have a very complex behavior.\\
		
		\paragraph{Model based\\}
		Models the world. It acts reactively based on the model (internal representation). The advantage is, it can consider aspects of the world that it currently can't observe, but it must maintain an internal representation.\\
		
		\paragraph{Goal based\\}
		Maintains a representation of how to act in order to achieve a specific goal. Often this means that the agent models both the environment and the goal. (There are also other techniques where the environment is not modeled.\\
		
		\paragraph{Utility based\\}
		There are more or less good ways to reach the goal. For example taxi driver (\textit{cf slide 42}). These statements describe the utility of being in certain states.
		\begin{itemize}
			\item Are formulated as a utility function
			\item Statements may have different priority (more important to not hit pedestrians than to drive fast).	
		\end{itemize}
		
		\paragraph{Goal and utility\\}
		The goal representation and the utility function can be seen as internalization of the performance measure. It changes with environment. The performance measure and utility function must be in agreement.\\
		An explicit utility function usually returns a numeric value representing the utility for a given state. Even if the agent does not have an explicit utility function, it must in some way implement these mechanism in order to behavior ...
		
		\paragraph{Learning agents\\}
		\textit{cf slide 44}
		Critic is an implementation of measure performance. It tells if the agent is working well or can do better.
		
		\subsection{Representations}

			\paragraph{Atomic representation\\}
			\begin{itemize}
				\item States as discrete entities
				\item No relation between states
				\item We can't speak about the distance between A and B \textit{cf slide}
			\end{itemize}							
			
			\paragraph{Factored representations\\}
			\begin{itemize}
				\item States are positions in a state space
				\item States are a set of values of the dimensions of the state space
				\item States have relative distance
			\end{itemize}
			
			\paragraph{Structured representations\\}
			\begin{itemize}
				\item States as discrete entities
				\item No relation between states
				\item We can't speak about the distance between state A and B
			\end{itemize}
			
			The structured representations are the most expressive. But more expressive representations also has drawbacks (more complex, more domain specific). There are in practice many mixes between atomic, featured and structured representation		